A research topic of considerable practical importance is the development of efficient schemes for coupling light to optical modes of topological nature. The fact that this is by no means a trivial challenge, can be understood from the following example. Thus, by employing photonic valley-Hall effects, one can design optical waveguiding structures supporting valley-momentum-locked modes localized at the interface between two domains characterized by different valley Chern numbers [1]}. To excite these topological modes, one usually places a point-like source near the interface between the two domains so that the interface mode is excited and subsequently measured. In practice, however, this approach can be very ineffective, chiefly for two reasons. First, in addition to the topological mode, the interface can support regular modes, too, and these regular modes are generally excited together with the topological mode. Second, using a point-like source to excite an optical mode can be a rather inefficient approach, as the spatial overlap between the source field and the optical mode can be rather limited.
